September 12, 2016 Leave a comment
My external powered speakers emit a loud, annoying hum if I plug them into the headphones socket of my Clevo W230SS laptop. The hum stops if I unplug the laptop’s mains charger, so the problem is due to an earth loop (a.k.a. ‘ground loop’). The charger’s recessed socket for connecting its mains lead has three prongs (IEC 60320 C6), i.e. the charger is not double-insulated. The recessed socket on a double-insulated mains charger would only have two prongs (IEC 60320 C8), and the label on a double-insulated charger in the UK usually has an icon consisting of two concentric squares. I suspect the audio circuitry in the Clevo W230SS is not very well designed, as there is virtually no hum from the same powered speakers if I plug them into the headphones socket of my Compal NBLB2 laptop while its mains charger, which has the same IEC 60320 C5/C6 coupler design as the Clevo laptop’s charger, is connected.
Now, I could have purchased a ground loop isolator, a passive device which is basically a couple of transformers (one per stereo channel), to interpose between the headphones socket on my laptop and the external powered speakers.
The YouTube video Solving Laptop Noise and Ground Loop Audio Interference contains a demonstration of what happens when you use a ground loop isolator on the headphones output of a laptop, and what happens when you use a double-insulated mains charger (two-prong coupler, rather than three-prong).
However, rather than buy a ground loop isolator I decided to try an active device, and purchased the XQ-10 portable headphones amplifier manufactured by Chinese company xDuoo. The XQ-10 is compact, fitting in the palm of my hand and weighing only 30 grammes. It has an aluminium-alloy case, and looks and feels well-made. Two cables are supplied: a USB cable to connect the XQ-10 to a phone charger or laptop in order to charge the LiPo battery in the XQ-10 (about 2 hours to charge, and about 20 hours of use on battery power), and a short 3.5 mm jack cable (male jack at both ends) to connect the XQ-10 to your laptop or phone.
If the XQ-10’s USB charging cable is not connected (see the photograph above) then the loud hum from my external powered speakers still occurs. But with both cables connected (see the photograph below), the XQ-10 does the job perfectly: there is no hum or hiss, even when I turn the speakers’ volume knob to maximum.
Although I do not need to use a headphones amplifier with the laptop when I use headphones or earphones — the volume is fine and there is no hum from headphones/earphones — I should mention that audio quality from my headphones and earphones connected to the XQ-10 is excellent (both with and without the USB charging cable connected, which is not surprising given that no earth loop exists when headphones/earphones are connected).
By the way, shop around if you do decide to buy the XQ-10, because its price on-line varies a lot. I paid GBP 17.95 for mine, and that included p&p.